1. Technical Field
An aspect of the present invention relates to an image encoding device, an image decoding device, and an integrated circuit device.
2. Related Art
JP-A-2000-92332 is a first example, JP-A-9-83809 is a second example, JP-A-2004-104624 is a third example, and JP-A-2001-257888 is a fourth example of related art that disclose the image encoding device and the image decoding device. The image encoding device disclosed in the first to the third examples, since an image inputted in raster order is encoded in units of a small block, a blocking method is required. Similarly, the image decoding device disclosed in the first to the third examples requires a deblocking method for returning the image encoded in units of a black in raster order.
In the blocking method and the deblocking method, for example, a block line memory shown in FIG. 10 of the second example of related art is required, thereby cost is increased.
In the first example, an image is divided into small blocks, and Hadamard transform and a discrete cosine transform (DCT) are performed so that a conversion coefficient is nonlinear quantized. Accordingly, if the block includes an edge where gray scale varies greatly, a quantized error caused by a high frequency component of the edge part is dispersed to all pixels in the block. As a result, deterioration of image quality becomes conspicuous especially in graphic-type (e.g., an image including characters, a map image, and the like).
In the fourth example, since a difference between a local decoding pixel value of a previous pixel and an object pixel is nonlinear quantized per element component, the nonlinear quantization is adversely affected of a quantized error of the previous pixel that is locally decoded. As a brief example, an original image shown in FIG. 17A is encoded so as to obtain a decoded image shown in FIG. 17B will be described. In the original image shown in FIG. 17A, a uniform longitudinal stripe pattern LSP and the left side of the longitudinal stripe pattern LSP have a different pixel value of a line n from other lines. In this case, when a pixel (n, m), positioned in the line n and the longitudinal stripe pattern, is encoded, a value of a locally decoded previous pixel (n, m−1) is different from values of other lines, lines n−1 and n+1. Therefore, a decoded image of the pixels (n, m), (n, m+1), and the like, positioned in the line n shown in FIG. 17B, has a quantization noise that is different from a quantization noise of other lines, the lines n−1, n+1, and the like. As a result, deterioration of image quality becomes conspicuous when the deterioration of image quality is compared with that of a decoded image of other lines, the lines n−1, n+1.